In an elevator system, one or more cars travel up and down the length of the elevator run, moving between the floors of the building carrying passengers.
In order to, inter alia, stop smoothly and level with the landing at each floor, it is important to know the precise location of the car at all times. To provide this information to the elevator controller system, a digital readout device known as a Primary Position Transducer or "PPT" is used.
For mid- and low-rise installations, a reader device mounted on the car and a vertical steel tape that runs the length of the hoistway are used to establish the car's position. Either steel vanes and/or magnets are mounted on the tape at precise locations with respect to the floor level of each landing.
For an example of a prior art position transducer system used with an elevator system, note assignee's U.S. Pat. No. 4,384,275 entitled "High Resolution and Wide Range Shaft Position Transducer Systems" of Masel et al issued May 17, 1983, the disclosure of which is incorporated herein by reference. In the patent two rotary position transducers are coupled to each other and to the shaft being rotated. Both of the transducers include one or more coded disks having sensing indicia forming tracks thereon that rotate a plurality of times in response to the rotations of the shaft, one of the transducers rotating at a different speed than the other. Each transducer produces signals, which are individual to the respective transducer and are the same for each rotation of the respective transducer.
The Masel patent includes:
sensing means related to each track for sensing the indicia thereon to provide signals indicative of the rotation of the disk from a rotational reference position; and PA1 signal processing means interconnected to the sensing means responsive to the signals corresponding to the coded tracks for providing a binary signal representation of the angular position of the disk and responsive to the signals corresponding to the coded tracks to provide, as a function of the number of coded track indicia which have been senses indicated thereby, a binary signal representation of the number of revolutions that the disk has rotated from the rotational reference position. PA1 1. An incremental system using a single encoder disk and two or more read heads. PA1 2. A quasi-absolute system using differential gearing that is capable of two independent position and speed signals. PA1 3. An absolute system, including a main disk attached to said input shaft; additional absolute encoders coupled to the input shaft through gears determining the turns of the main shaft; and at least two independent position and velocity output signals being obtained with the use of independent sets of read heads located circumferentially about each disk, a primary output signal being used to run the elevator and the other, secondary, output signal being used for normal terminal protection for the elevator car travel. A combination of the primary and secondary velocity signals may be used to derive a door zone speed check signal in compliance with the ANSI A-17.1 Elevator Code, which requires that an independent means be used to check speed in the door zone. By equipping the system with a third set of sensors, it is possible to obtain an independent position signal useful for verifying that the elevator is in the door zone before the doors are opened. PA1 normal position control; PA1 normal terminal protection; and PA1 door zone protection.
Some additional patents which may be of interest are U.S. Pat. No. 4,041,483 entitled "Absolute Incremental Hybrid Shaft Position Encoder" of Groff issued Aug. 9, 1977; and U.S. Pat. No. 3,885,209 entitled "Two Speed Control System" of Lazarus issued May 20, 1975. In the latter patent first and second transducers are connected to first and second rotatable shafts, respectively, with the shafts coupled to each other through a single mesh of gears. The transducers are electrically coupled in cascade to enable the first to provide a "fine" indication of the angular position of the first shaft, while the second provides a "coarse" indication of the number of revolutions of the same first shaft.